1. Technical Field
This invention relates generally to the use of ISO corner fittings in composite material structures, and particularly to an apparatus and method for facilitating maintenance of such ISO corner fittings in composite material structures.
2. Description of the Related Art
An ISO (International Standards Organization) container is a freight or shipping container that complies with relevant ISO container standards, such as ISO 668 (5th edition) and ISO 1496-3 (4th edition). For examples of ISO shipping containers, see U.S. Pat. Nos. 4,231,709; 4,940,252; and 6,012,598, which are hereby incorporated by reference.
Heretofore, manufacturers of ISO shipping containers have used metal framework with steel or aluminum sheathed panels made of composition board or other materials attached to the framework by bolts, rivets or welding. Corner fittings are then attached, in accordance with ISO standards, to each corner of the shipping container. The ISO corner fittings are used to secure cables and other components to the shipping containers during loading and unloading of the containers, as well as to secure the containers to one another and to the transport vehicle. Consequently, the attachment between the corner fitting and the shipping container must be able to support the entire weight of the shipping container plus any cargo therein. For containers that are transported by air lift, the ISO corner fittings must further be able to support the dynamic load imposed during the air lift, which is typically about three times that of the static load.
Due to the tremendous loads routinely placed on the ISO corner fittings, these components sustain a significant amount of wear and tear damage. Use of damaged and/or worn ISO corner fittings presents a safety risk that can have disastrous consequences. For example, in applications that require the shipping container to be lifted or hoisted in the air, a damaged and/or worn ISO corner fitting can result in the container being dropped. Therefore, it is absolutely vital that maintenance be performed regularly and frequently on the ISO corner fittings to repair or replace damaged and/or worn fittings. Regular maintenance and repair helps keep the ISO corner fittings in good operating condition and can extend the service life of the much more expensive and harder to replace shipping containers.
A primary consideration in determining how often maintenance and repair is performed is the attachability and detachability of the ISO corner fittings. If the ISO corner fittings can be easily detached from and reattached to the shipping containers, it will take less time, effort, and costs to perform maintenance and repair. As a result, the ISO corner fittings are more likely to have frequent maintenance and repair and be kept in good operating condition. On the other hand, if the ISO corner fittings are difficult to remove and reattach, maintenance and repair is less likely to be performed very frequently and the ISO corner fittings are more likely to be in poor operating condition.
A number of techniques exists for attaching an ISO corner fitting to a shipping container. FIG. 1 illustrates an example of a prior part attachment technique. As can be seen, an ISO corner fitting 100 is formed in a rectangular box shape with openings or eyelets 102 formed on three of the surfaces thereof. The ISO corner fitting 100 is usually oriented so that the eyelet surfaces are exposed when the corner fitting is mounted on the shipping container. Various attachments can then be attached to the eyelets 102 to facilitate lifting, moving, loading, lockdown, and off-loading of the containers. A steel, cast iron or aluminum extension 104 is welded to the bottom (or top) surface of the corner fitting 100, which is itself also made of steel or cast iron. The extension 104 has a number of holes 106 formed therein through which bolts or rivets may be driven to attach the ISO corner fitting 100 to the shipping container. In some cases, a steel or cast iron flange 108 may also be welded to the inner or unexposed side surfaces of the ISO corner fitting 100. The flange 108 also has a number of holes 110 formed therein through which bolts or rivets may be driven to strengthen the attachment between the corner fitting 100 and the shipping container.
The above attachment technique works reasonably well if one is using the metal frame and panel type shipping containers. The problem with using the metal frame and panel type shipping containers is they are very heavy. For example, a standard 20′ long container constructed to meet ISO size requirements (typically 8′ wide×8′ high) weighs on the order of 4,000 to 5,000 lbs. The heavier weight of these containers limits the maximum cargo weight, or payload, that can be transported in such a container. The heavier weight also increases the transportation costs in terms of reduced gas mileage and excess wear and tear damage on the transport equipment.
Metal frame and panel shipping containers have another drawback in that a difference in the thermal expansion characteristics of the various materials used in the construction of the containers can cause the metal framework to expand or contract at different rates than the panels. The difference in thermal expansion characteristics is particularly significant in extreme temperature environments where the joints between the panels and the metal frame can become stressed or cracked, permitting moisture and water to enter into the joint. Also, for panels that have a metal surface over a nonmetallic core, the metal surface tends to expand and contract at a different rate than the underlying nonmetallic core, resulting in possible delamination of the panel.
Corrosion is another problem for metal-framed shipping containers, especially in marine and industrial environments. Moisture can cause the metal frame and panels to rust, possibly causing separation at the various joints thereof. Certain chemicals can cause corrosion of the metal frame and panels, thereby compromising the structural integrity of the shipping container.
Shipping containers that are made of composite material, on the other hand, have been shown to be far superior to the metal-framed shipping containers in the above respects. For purposes of this description, the term “composite material” refers to any type of reinforced polymer or epoxy material. The reinforcing material may be a woven or non-woven fiber material such as glass fibers or carbon fibers that are then coated with a polymer or an epoxy. Other high strength materials such as Kevlar® may also be used to is reinforce the composite material. Such composite materials are well known and may be available from, for example, Creative Protrusion, Inc. of Alum Bank, Pa., Advanced Composite Materials, Inc. of Eureka Springs, Ark., and Zoltek Corporation of St. Louis, Mo. Shipping containers made of such composite materials have been shown to have higher load bearing capacity than their metal-framed counterparts, yet are lighter in weight. This lighter weight will increase the amount of cargo that can be carried in the shipping containers, while at the same time reduce the cost of transporting the containers. Composite material structures have also been shown to be more resistant to corrosion and rust, making the containers more suitable for use in marine and other hostile environments. In addition, the composite material renders the structures virtually invisible to detection by radar, an extremely desirable quality for applications that require stealth (e.g., military or intelligence gathering applications). By the same token, the composite material does not impede reception or transmission of radio waves and, therefore, will not prohibit or interfere with radio communication to and from the structure.
Presently, however, there is no way to quickly and easily attach and detach an ISO corner fitting to and from a shipping container made of composite material. The ability to quickly and easily attach and detach the ISO corner fitting, as mentioned above, is of key importance in facilitating maintenance and repair of the ISO corner fittings. Existing attachment techniques, such as the one shown in FIG. 1, would not work well with composite material shipping containers. The bolts or rivets holding the ISO corner fitting in place would likely rip right through the lighter weight composite material when any significant load is applied. Even assuming these techniques could be used with composite material shipping containers, maintenance and repair would still be very difficult to perform. For example, the extension 104 and the flange 108 would have to be cut through to remove the ISO fitting. The ISO fitting would then have to be welded back on to the extension 104 and the flange 108 to reattach it. Welding, however, is highly ill-advised once the composite material is in place, as the heat from a blow torch may severely damage the composite material. Alternatively, each of the bolts or rivets holding the ISO corner fitting in place could be completely removed and the entire assembly be detached. The same process would have to be performed in reverse in order to reattach the ISO corner fitting. This entire process, however, would not only be tedious, time consuming, impractical, and costly, but would also discourage frequent performance of maintenance and repair.
Accordingly, in order to take advantage of the many benefits of composite material shipping containers without compromising safety and reliability, what is needed is a way to easily attach and detach an ISO corner fitting to the composite material shipping container without welding, cutting, or taking apart the ISO corner fitting assembly.